During the manufacture of semiconductor wafers, the edge of the wafer is frequently ground to a rounded or beveled profile by means of an abrasive wheel. The rounded edge reduces chipping during later process steps. The grinding wheel usually contains a diamond abrasive ranging in particle size from 30 to 40 micrometers, and leaves a surface that has visible ridges and valleys as seen under a low power microscope.
A smoother edge surface may he required for manufacturing some integrated circuits than may he provided on edge-ground wafers. Smoother edges are desirable because wafers with rough edges may chip more easily. Additionally edge-ground wafers may contain deeper microcracks than edge-polished wafers, and edge-ground wafers may contain depressions that may be a source of particles in processes that use phosphorus glasses. Edge-ground wafers may cause further resist to form "beaded" edges, i.e., photo resist may not spin correctly to make a uniform layer at the edge of the wafer, but may make an irregular thickened bead around the wafer edge. If this beaded edge is formed, it may cause problems such as particle formation.
Present polishing processes include mechanically abrading wafers with a finer abrasive, dipping the wafer in an acid polishing mixture, treating wafer edges with an acid polishing mixture or by dripping or spraying etchant on to the edge. Mechanical abrasion may have the disadvantage that it does not produce a mirror finish. Dipping the entire wafer in acid may lead to the rounding of the planar surfaces of the wafer unless extreme care is exercised in the process. Acid etching of the edge may have the disadvantage of requiring considerable removal of material to etch a smooth surface, which may cause a problem with maintaining an optimum profile for the wafer.
Wafers are frequently processed as single wafers. Individual processing of single wafers is time-consuming and costly. Some edge polishers carry wafers between threaded shafts, but these wafers have to be individually loaded and unloaded.